There's a plethora of providers in Push-to-Talk (PTT), Voice-over-IP (VoIP) and similar communication software for a few operating system platforms already on the market, i.e. Windows Mobile, Android and S60. These operators focus on the usability of a mobile device itself as a stand-alone communication device and conjecture that a user interacts with a communication application solely through the mobile device's built-in user interface, typically nowadays a keypad or a touch screen.
To support a certain accessory such as a certain RSM device, each application developer would in practice be required to modify their software in co-operation with the RSM device manufacturer. This is unfeasible while tens of these applications developers would needed to be persuaded to support each potential device by the RSM manufacturers.
For example, sending PTT commands over a Bluetooth (BT) link is not supported by the existing BT standards. An RSM device thus needs specific firmware and software to generate PTT commands understood by a predetermined communication application like Push to Talk over Cellular (PoC) application running on the applied mobile device. Correspondingly, the PoC-application requires RSM manufacturer-specific support to be able to interpret the received proprietary commands.